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To:     Noah Goldstein <goldstein.w.n@gmail.com>
Cc:     noah <goldstein.n@wustl.edu>, Jens Axboe <axboe@kernel.dk>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   Pavel Begunkov <asml.silence@gmail.com>
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Subject: Re: [PATCH] fs: io_uring.c: Add skip option for __io_sqe_files_update
Message-ID: <32c9ce7e-569d-3f94-535e-00e072de772e@gmail.com>
Date:   Tue, 26 Jan 2021 12:26:02 +0000
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On 22/12/2020 02:10, Noah Goldstein wrote:
> On Sun, Dec 20, 2020 at 03:18:05PM +0000, Pavel Begunkov wrote:
>> On 20/12/2020 06:50, noah wrote:> From: noah <goldstein.n@wustl.edu>
>>>
>>> This patch makes it so that specify a file descriptor value of -2 will
>>> skip updating the corresponding fixed file index.
>>>
>>> This will allow for users to reduce the number of syscalls necessary
>>> to update a sparse file range when using the fixed file option.
>>
>> Answering the github thread -- it's indeed a simple change, I had it the
>> same day you posted the issue. See below it's a bit cleaner. However, I
>> want to first review "io_uring: buffer registration enhancements", and
>> if it's good, for easier merging/etc I'd rather prefer to let it go
>> first (even if partially).

Noah, want to give it a try? I've just sent a prep patch, with it you
can implement it cleaner with one continue.

>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 941fe9b64fd9..b3ae9d5da17e 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -7847,9 +7847,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>>  	if (IS_ERR(ref_node))
>>  		return PTR_ERR(ref_node);
>>  
>> -	done = 0;
>>  	fds = u64_to_user_ptr(up->fds);
>> -	while (nr_args) {
>> +	for (done = 0; done < nr_args; done++) {
>>  		struct fixed_file_table *table;
>>  		unsigned index;
>>  
>> @@ -7858,7 +7857,10 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>>  			err = -EFAULT;
>>  			break;
>>  		}
>> -		i = array_index_nospec(up->offset, ctx->nr_user_files);
>> +		if (fd == IORING_REGISTER_FILES_SKIP)
>> +			continue;
>> +
>> +		i = array_index_nospec(up->offset + done, ctx->nr_user_files);
>>  		table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
>>  		index = i & IORING_FILE_TABLE_MASK;
>>  		if (table->files[index]) {
>> @@ -7896,9 +7898,6 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>>  				break;
>>  			}
>>  		}
>> -		nr_args--;
>> -		done++;
>> -		up->offset++;
>>  	}
>>  
>>  	if (needs_switch) {

-- 
Pavel Begunkov